Project Summary/Abstract Acute myeloid leukemia (AML) is maintained by a small minority of self-renewing leukemic stem cells (LSCs). Defining and targeting the key molecules that specifically regulate LSCs might eradicate AML. Heat shock transcription factor 1 (HSF1) is known to regulate the expression of heat shock proteins (HSPs) to protect cells from misfolded protein-induced proteotoxic stress. Although HSF1 is not an oncogene, it enables cancer cells to accommodate imbalances in signaling and alterations in DNA, protein, and energy metabolism, a phenomenon called ?non-oncogene addiction?. Targeting HSPs in AML is being explored with promising results. However, targeting HSPs induces feedback that increases HSF1 activity, which may compromise treatment effects. Therefore, targeting HSF1 directly may be a more attractive alternative. However, given the critical roles of HSF1 in the maintenance of normal cellular homeostasis, targeting HSF1 could adversely affect normal hematopoiesis. Unexpectedly, our preliminary data show that HSF1 is dispensable for normal hematopoiesis, but specifically required for the self-renewal of LSCs. Mechanistically, deletion of HSF1 disrupts amino acid metabolism and mitochondrial oxidative phosphorylation (OXPHOS), which plays a critical role in regulating LSC function, and dysregulates multifaceted genes involved in LSC stemness. In addition, we identified that hepatocyte nuclear factor 4a (HNF4a) as a direct HSF1 target. Overexpression of HNF4a largely reconstitutes deletion of HSF1-induced impaired LSC function. Based on these observations, we hypothesize that HSF1 is specifically required for LSC self-renewal through regulating leukemic energy metabolism (mainly OXPHOS) and is a potential therapeutic target in AML. We propose the following two specific aims to test our hypothesis. Aim 1: To determine the underlying mechanism whereby HSF1 is specifically required for LSC self-renewal. We will determine 1) the impact of HSF1 ablation on LSC frequencies, proliferation and OXPHOS; 2) the HSF1 transcriptional targets in LSCs by comprehensive analysis of transcriptomic gene expression, chromatin accessibility and chromatin immunoprecipitation (ChIP) sequencing in the presence or absence of HSF1; 3) how HNF4a reconstitutes HSF1 ablation-induced LSC defects, especially the effect of HNF4a on OXPHOS; and 4) if deletion of HSF1 impairs mechanistically different types of AML. Aim 2: To determine if targeting HSF1 effectively eliminate human LSCs. We will determine 1) the impact of HSF1 inhibition on human LSC proliferation, apoptosis, self-renewal and oxidative phosphorylation; 2) the HSF1- dependent regulatory circuitry in human LSCs; and 3) if the expression of HSF1 protein correlates with AML therapeutic response and relapse. The expected outcomes of this comprehensive analysis are identification of the mechanism whereby HSF1 specifically regulates LSC self-renewal, providing the rationale for targeting HSF1 and using HSF1 to monitor AML progression.